This invention relates to a method and an apparatus for examining a fiber web advanced in a fiber processing machine such as a card or a roller card unit. The material of the web is cotton, chemical fibers or the like. The fiber web has useful fibers with intermediate, empty spaces therebetween (hereafter also referred to as empty locations). The apparatus includes a measuring track for the fiber material. The measuring track is associated with a camera, such as a diode matrix camera which is connected with an evaluating device such as an image processing computer.
German Offenlegungsschrift (application published without examination) 39 28 279 to which corresponds U.S. Pat. No. 5,130,559, describes an apparatus in which foreign particles are recognized in the fiber flow in order to determine the degree of soiling (trash content) of the fiber material by optical and electronic means. For this purpose a sensor detects each foreign individual particle in the running fiber web and, by means of an evaluating device, for each individual particle specific characterizing magnitudes are determined (particularly gray scale and edge detection) to identify the matter as a foreign particle. In this manner, the foreign particles are differentiated from the useful fibers. The foreign particles form locally sharply delimited defective locations which are concentrated in a very small space. Further, such foreign particles display a different behavior with respect to the useful fibers; for example, neps (fiber knots which have a diameter less than 1 mm) appear as dots of increased reflection and may therefore be separated from the other signals. The individual particles are determined as differing from the remaining fiber web which only represents a background. The smaller the selection of the scanned surface region of the fiber web, the more conspicuous the appearance of a nep.
It is a disadvantage of the above-outlined conventional arrangement that a detection and determination of the degree of homogeneity of the fiber web is not feasible. Also, such conventional arrangement is not concerned with a determination of the distribution and orientation of the useful fibers.